Abstract
AbstractIn this work, it is shown how different carrier recombination paths significantly broaden the photoluminescence (PL) emission bandwidth observed in type‐II self‐assembled SiGe/Si(001) quantum dots (QDs). QDs grown by molecular beam epitaxy with very homogeneous size distribution, onion‐shaped composition profile, and Si capping layer thicknesses varying from 0 to 1100 nm are utilized to assess the optical carrier‐recombination paths. By using high‐energy photons for PL excitation, electron‐hole pairs can be selectively generated either above or below the QD layer and, thus, clearly access two radiative carrier recombination channels. Fitting the charge carrier capture‐, loss‐ and recombination‐dynamics to PL time‐decay curves measured for different experimental configurations allows to obtain quantitative information of carrier capture‐, excitonic‐emission‐, and Auger‐recombination rates in this type‐II nano‐system.
Highlights
Improvements of the optical properties of SiGe QDs, for example, with respect significantly broaden the photoluminescence (PL) emission bandwidth to emission linewidth and intensity, were observed in type-II self-assembled SiGe/Si(001) quantum dots (QDs)
From the evaluation of two large-area images of 5 × 5 μm2 size, we find that 98.8% of the QDs are of dome-shape[46] with an average height of 30.6 ± 1.8 nm and a respective volume of 2.0
We stress that the molecular beam epitaxy (MBE) growth conditions chosen in this work for QD growth are closer to thermal equilibrium, and result in onion shape composition profiles, supporting the results found by Georgiou et al.[56]
Summary
The growth of the samples was carried out on high-resistivity (>1000 cm) Si(001) substrates in a Riber Siva 45 solid source molecular beam epitaxy (MBE) facility. Seven monolayers (ML) of Ge were deposited at 750 °C and at a growth rate of 0.05 As−1 For time-resolved measurements, we excited the samples by a pulsed laser (wavelength λ = 442 nm), with a pulse width of ࣈ200 ps and an average optical power ranging from 240 to 2900 nW in a laser spot of ࣈ2 μm diameter at a repetition rate of 1 MHz. The time-delay between excitation pulse and PL photon detection was measured by a superconducting single photon detector (SSPD) from Scontel operated at 1.8 K connected to a PicoQuant time correlator. The time jitter of the SSPD was ࣈ30 ps so that the time resolution of the setup used in this work was limited by the laser pulse width
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